This from the Jan 21st 2012 edition of The Economist:
ONE sure giveaway of quack medicine is the claim that a product can treat any ailment. There are, sadly, no panaceas. But some things come close, and exercise is one of them. As doctors never tire of reminding people, exercise protects against a host of illnesses, from heart attacks and dementia to diabetes and infection.
Full The Economist Article: Exercise and longevity: Worth all the sweat | The Economist.